Tip clearance control with finned case design

ABSTRACT

An apparatus and methods for controlling tip clearance in gas turbine engines may be provided. The apparatus and methods may include situating fins on a surface of a turbine case included in a turbine section of the gas turbine engine. The fins may act as a means for maintaining tip clearance by, for example, controlling the thermal expansion of the turbine case. The turbine case may shroud turbine blades, and the turbine blades may include tips at a radial end of the blades. During operation of the gas turbine engine, the clearance between the tips and the turbine case is desirably as small as possible while avoiding contact in order to optimize efficiency of the gas turbine engine.

TECHNICAL FIELD

This disclosure relates to gas turbine engines and, in particular, toturbine cases.

BACKGROUND

An aircraft, such as a helicopter, a tilt-rotor aircraft, or a plane,may have a gas turbine engine that includes turbine blades spinningwithin a turbine case. Efficiency of the turbine engine may depend, inpart, on the proximity of tips of the turbine blades to the case duringoperation of the gas turbine engine.

BRIEF DESCRIPTION OF THE DRAWINGS

The embodiments may be better understood with reference to the followingdrawings and description. The components in the figures are notnecessarily to scale. Moreover, in the figures, like-referenced numeralsdesignate corresponding parts throughout the different views.

FIG. 1 illustrates an example of a gas turbine engine system including aturbine section;

FIG. 2 illustrates an isometric view of an example of a portion of aturbine section including a turbine case including fins, the fins shapedas pins;

FIG. 3 illustrates a side view of the turbine case example shown in FIG.2;

FIG. 4 illustrates an isometric view of an example of a portion of aturbine section including a turbine case including fins, the fins shapedas wedges;

FIG. 5 illustrates a side view of the turbine case example shown in FIG.4;

FIG. 6 illustrates an isometric view of an example of a portion of aturbine section including a turbine case including fins, the fins shapedas rectangular slabs of varying length;

FIG. 7 illustrates a side view of the turbine case example shown in FIG.6;

FIG. 8 illustrates a side view of a turbine case having fins on radiallyinward structures supporting a blade track.

DETAILED DESCRIPTION

By way of an introductory example, a portion of a turbine section of agas turbine engine including a turbine case having one or more fins isprovided for use in a gas turbine engine. The fins may provide a meansfor maintaining tip clearance between turbine blade tips and a bladetrack in the turbine section. The fins may be situated on a surface of aturbine case or on structures radially inward from the surface of theturbine case in order to, for example, provide a means of thermalcommunication between an ambient fluid, such as air, and the turbinecase.

One interesting feature of the systems and methods described below maybe that the fins on the turbine case may facilitate control of theclearance between the turbine blades and the blade track duringoperation of an engine, thereby increasing efficiency of the engine.Alternatively, or in addition, an interesting feature of the systems andmethods described below may be that facilitating the control of the tipclearance may help avoid the turbine blades contacting the blade trackand causing wear on the tips of the turbine blades.

FIG. 1 illustrates a cross-sectional view of a gas turbine engine 100for propulsion of, for example, an aircraft. Alternatively or inaddition, the gas turbine engine 100 may be used to drive a propeller inaquatic applications, or to drive a generator in energy applications.The gas turbine engine 100 may include an intake section 120, acompressor section 160, a combustion section 130, a turbine section 110,and an exhaust section 150. During operation of the gas turbine engine100, fluid received from the intake section 120, such as air, travelsalong the axial direction D1 and may be compressed within the compressorsection 160. The compressed fluid may then be mixed with fuel and themixture may be burned in the combustion section 130. The combustionsection 130 may include any suitable fuel injection and combustionmechanisms. The hot, high pressure fluid may then pass through theturbine section 110 to extract energy from the fluid and cause a turbineshaft of a turbine 114 in the turbine section 110 to rotate, which inturn drives the compressor section 160. Discharge fluid may exit theexhaust section 150.

As noted above, the hot, high pressure fluid passes through the turbinesection 110 during operation of the gas turbine engine 100. As the fluidflows through the turbine section 110, the fluid passes between adjacentblades 112 of the turbine 114 causing the turbine 114 to rotate. Therotating turbine 114 may turn a shaft 140 in a rotational direction D2,for example. The blades 112 may rotate around an axis of rotation, whichmay correspond to a centerline X of the turbine 114 in some examples.

FIG. 2 illustrates an isometric view of an example of a portion of theturbine section 110 that comprises a turbine case 210 including fins 220having a pin shape. The turbine case 210 may include, for example, aradially outward facing surface 212, an aft section 216 and a foresection 218, the fin 220, and a flange 250. As noted above, duringoperation of the gas turbine engine 100, fluid may pass between adjacentblades 112 causing the blades 112 to rotate in the rotational directionD2 in some examples or in a direction opposite of the rotationaldirection D2 in other examples.

During operation of the gas turbine engine 100, the turbine case 210 maybe subjected to a large amount of heat from a variety of sources. Thisheat may be absorbed into the turbine case 210 in a significant enoughquantity to cause the turbine case 210 to substantially expand,resulting in an increase in a tip clearance 240. For example, theturbine case 210 may experience varying amounts of heat absorbed fromoperation of the gas turbine engine 100 at various stages of operationof the gas turbine engine 100. Examples of the various stages ofoperation may be, but are not limited to: idle, take-off, climb, cruise,descent, landing, and idle after landing. Referring to FIG. 3, the tipclearance 240 is preferably, during the various stages of operation,only as large as necessary to avoid contact between the blades 112 (moreprecisely, the tips 230 of the blades 112) and the radially inwardfacing surface 264 of the blade track 260. If the tip clearance 240becomes larger than is needed to avoid the tips 230 contacting theradially inward facing surface 264 of the blade track 260, then it maybe undesirable because, for example, the excessive tip clearance 240allows fluid, such as gas, moving through the turbine section 110 topass through the tip clearance 240 instead of past an airfoil portion ofthe turbine blades 112. If the fluid passes through the tip clearance240, it results in a decreased overall efficiency of the gas turbineengine 100.

The turbine case 210 may include a shell surrounding the turbine blades112. Alternatively or in addition, the turbine case 210 may include aring-shaped body in which the turbine blades 112 are configured torotate. During operation of the gas turbine engine 100, the turbine case210 may surround fluid moving through the turbine section 110 of the gasturbine engine 100, thus promoting contact between the fluid and theblades 112. The turbine case 210 may include a variety of features, suchas for example, a flange 250.

In some examples the turbine case 210 may be made of metal or metalalloy. Alternatively, or in addition, the turbine case 210 may made froma ceramic matric composite (“CMC”). In some examples, the turbine case210 may taper smoothly along the axial direction D1 from the aft section216 to the fore section 218, or vice versa. Alternatively or inaddition, the turbine case 210 may be tapered along the axial directionD1 from the aft section 216 to the fore section 218, or vice versa, in atiered fashion.

The fins 220 may be protrusions extending radially from the turbine case210. The fins 220 may be in thermal communication with the turbine case210. The fins 220 may be integral to the turbine case 210.Alternatively, the fins 220 may be coupled to the turbine case 210. Thefins 220 may exchange heat between the turbine case 210 and, forexample, an ambient fluid, such as cooling air. The fins 220 may haveany shape or combination of shapes. For example, the fins 220 may bepins, wedges 320, rectangular slabs, polyhedrons, or non-polyhedrons.

In some examples, the fins 220 may be distributed uniformly or,alternatively, non-uniformly along either the radially outward facingsurface 212 of the turbine case 212, structures 270 located radiallyinward from the turbine case 212, or both. If the fins 220 are along thestructures 270 located radially inward from the turbine case 212, astream of cooling fluid may be present with the fins 220 to allow forthermal communication between the cooling fluid and the fins 220.Alternatively or in addition, a variety of shapes of the fins 220 may beutilized in a single example. For example, the fins 220 may include pinsand wedges, and both may be present on the turbine case 210.

In some examples, portions of the turbine case 210 may have a higherlocal thermal inertia than other portions. Thermal inertia may be thedegree of slowness with which the temperature of a body approaches thatof its surroundings. This difference in local thermal inertia may be dueto, for example, differences in local material, local thickness T of theturbine case 210, proximity to features of the turbine case 210, such asthe flange 250, or other reasons.

The turbine case 210 may have different local thermal inertias at somepoints of the turbine case 210. Additionally, these portions may havedifferent mean local thermal inertias. For example, a portion of theturbine case 210 that includes the flange 250 may have a higher meanthermal inertia than a portion of the turbine case 210 that is furtheraway from the flange 250. The location, the orientation, the size, andthe shape of the fins 220 (protrusions) may be selected to make thetemperature more uniform across portions of the turbine case 210. Forexample, if the fins 220 abut the flange 250 as shown in FIG. 4, such anarrangement may lower the thermal inertia of the portion of turbine case210 that includes the flange 250 so that the thermal inertia is closerto the thermal inertia of the portion of the turbine case 210 that isfurther away from the flange 250. If both portions of the turbine case210 are subjected to the same amount of heat, then the temperatures ofthe portions may be closer to each other as the turbine case 210 heatsand cools than the portions would have been without the fins 220.Accordingly, the fins 220 may include or be a means for maintaining thetip clearance 240.

Local thermal inertia may be the thermal inertia at a particular pointon the turbine case 210 while mean local thermal inertia may be theaverage thermal inertia in a portion of the turbine case 210. Despitedifferences in local thermal inertia or mean local thermal inertia, theturbine case 210 may obtain a substantial uniform temperature by variousmethods. An example of such a method may include distributing aplurality of fins 220 along the radially outer facing surface 212 atportions of the turbine case 210 in proportion with the local thermalinertia of the portions. Alternatively, or in addition, a method mayinclude varying the height of the fins 220 in proportion with the localthermal inertia of the portions of the turbine case 210. Alternatively,or in addition, a method may include a blower providing a fluid adjacentto the fins 220. The fluid may include liquid, gas, or both. The fluidmay be higher in temperature relative to the fins 220, thus transferringheat into the fins 220, or lower in temperature relative to the fins220, thus transferring heat from the fins 220. Examples of fluidsinclude, but are not limited to: ambient air from outside of the gasturbine engine 100, bleed air from the compressor section 160, or aliquid such as water, glycerin-based coolant, or other appropriateliquid coolant.

The flange 250 may be a protruding rim, edge, rib, or collar used tostrengthen the turbine case 210, hold in place the turbine case 210, orattach the turbine case 210 to another part of the gas turbine engine100. The flange 250 shown in FIG. 2 is situated at the end of the foresection 218 of the turbine case 210 without substantially extendingaxially along the radially outward facing surface 212 of the turbinecase 210. Alternatively, the flange 250 may be situated on the aftsection 216 of the turbine case 210. Alternatively, multiple flanges 250may be situated on various potions of the turbine case 210. Fins 220 maybe attached to the flange 250 and extend axially along the radiallyoutward facing surface 212 of the turbine case 210. Alternatively or inaddition, some or all of fins 220 may be completely separate from theflange 250.

FIG. 3 is a cross-sectional view of the turbine case 210 shown in FIG.2. FIG. 3 is an example of the turbine case 210 having the fins 220 inthe shape of pins. The pins may be, for example, cylindrical. The pinsmay vary in diameter, either within a single pin or in relation to otherpins or both.

The tip clearance 240 may exist between a tip 230 of a respective one ofthe blades 112 and a radially inward facing surface 264 of the bladetrack 260. The tip clearance 240 may fluctuate during operation of thegas turbine engine 100. The fins 220 may serve as a means formaintaining tip clearance 240. The means for maintaining tip clearance240 may change the mean local thermal inertia of portions of the turbinecase 210 and include protrusions shaped as pins, wedges, slabs,polyhedrons, or non-polyhedrons.

The turbine case 210 has the thickness T defined by a radial lengthbetween the radially outward facing surface 212 and the radially inwardfacing surface 214 of the turbine case 210. The thickness T may varyalong the axial direction D1.

FIG. 4 illustrates an isometric view of another example of a portion ofthe turbine case 210 that includes the fins 220 that are in the shape ofwedges. The wedges may extend radially from the turbine case 210resulting in the wedges having a wedge height 410 that may vary alongthe wedge length 420. The wedges may have varying wedge lengths 420 inrelation to each other. The wedges may have a constant tapering alongthe wedge length 420. Alternatively or in addition, the wedges may havenon-constant tapering.

FIG. 5 is a cross-sectional view of the turbine case 210 shown in FIG.4. FIG. 5 is an example of the turbine case 210 having fins 220 in theshape of wedges. The wedges may have, for example, a triangular crosssection. The wedges may abut the flange 250. Alternatively, the wedgesmay be situated along any portion in any direction of the radiallyoutward facing surface 212.

FIG. 6 illustrates an isometric view of another example of a portion theturbine case 210 that includes the fins 220. The fins 220 in thisexample are substantially rectangular slabs. The rectangular slabs mayhave a slab length 620. FIG. 6 shows a plurality of rectangular slabs.The rectangular slabs may have varying slab lengths 620 in relation toeach other. The rectangular slabs may abut the flange 250. Alternativelyor in addition, the rectangular slabs may be situated along any portionin any direction of the radially outward facing surface 212.

FIG. 7 is a cross-sectional view of the turbine case 210 shown in FIG.6. FIG. 7 is an example of the turbine case 210 having fins 220 in theshape of rectangular slabs.

FIG. 8 is a cross-sectional view of the turbine case 210 with the fins220 located on the structures 270 located radially inward from theturbine case 212. The structures 270 may be supporting the blade track260. Alternatively, the structures 270 may be independent of the bladetrack 260.

To clarify the use of and to hereby provide notice to the public, thephrases “at least one of <A>, <B>, . . . and <N>” or “at least one of<A>, <B>, . . . <N>, or combinations thereof” or “<A>, <B>, . . . and/or<N>” are defined by the Applicant in the broadest sense, superseding anyother implied definitions hereinbefore or hereinafter unless expresslyasserted by the Applicant to the contrary, to mean one or more elementsselected from the group comprising A, B, . . . and N. In other words,the phrases mean any combination of one or more of the elements A, B, .. . or N including any one element alone or the one element incombination with one or more of the other elements which may alsoinclude, in combination, additional elements not listed.

While various embodiments have been described, it will be apparent tothose of ordinary skill in the art that many more embodiments andimplementations are possible. Accordingly, the embodiments describedherein are examples, not the only possible embodiments andimplementations.

The subject-matter of the disclosure may also relate, among others, tothe following aspects:

-   1. An apparatus comprising:    -   a protrusion on a turbine case, the protrusion comprising a        means for maintaining a tip clearance, the tip clearance being a        space between a blade track and a tip of a turbine blade        configured to rotate within the turbine case.-   2. The apparatus of aspect 1, wherein the protrusion is included in    a plurality of protrusions on the turbine case that each comprise a    corresponding means for maintaining the tip clearance.-   3. The apparatus of aspect 2, wherein the protrusions comprise a    first protrusion and a second protrusion, the first protrusion    extends a first distance radially from the turbine case and the    second protrusion extends a second distance radially from the    turbine case, wherein the first distance is greater than the second    distance,    -   wherein the turbine case includes a first portion comprising a        first local mean thermal inertia and a second portion comprising        a second local mean thermal inertia, wherein the first local        mean thermal inertia is greater than the second local mean        thermal inertia, and    -   wherein the first protrusion is located on the first portion and        the second protrusion is located on the second portion.-   4. The apparatus of aspect 2, wherein the turbine case includes a    first portion comprising a first local mean thermal inertia and a    second portion comprising a second local mean thermal inertia,    wherein the first local mean thermal inertia is greater than the    second local mean thermal inertia, and wherein the first portion    comprises a greater number of protrusions than the second portion.-   5. The apparatus of aspect 1, wherein the protrusion has a height    and a length, and wherein the means for maintaining tip clearance is    configured to transfer heat from the turbine case to an ambient    fluid, the heat transfer occurring at a rate, the rate varying with    the height of the protrusion, the height varying along the length.-   6. The apparatus of aspect 1, wherein the protrusion is integral to    the turbine case.-   7. The apparatus of aspect 1, wherein the protrusion is a first    protrusion, and wherein a second protrusion comprising a means for    maintaining a tip clearance is situated on a structure supporting    the blade track, wherein the structure supporting the blade track is    located radially inward from the turbine case.-   8. An apparatus comprising:    -   a turbine case comprising a fin, wherein the fin comprises a        protrusion extending a height radially from the turbine case and        a width circumferentially along a surface of the turbine case,        the fin extending a length along an axial direction of the        turbine case, the length larger than the width.-   9. The apparatus of aspect 8, wherein the fin is included in a    plurality of fins, and the fins are distributed non-uniformly around    the case.-   10. The apparatus of aspect 8, wherein the fin extends radially    inwardly from the turbine case.-   11. The apparatus of aspect 8, wherein the fin extends radially    outwardly from the turbine case.-   12. The apparatus of aspect 8, wherein the height varies along the    length.-   13. The apparatus of aspect 8, wherein the fin is included in a    plurality of fins on the turbine case, wherein a first fin extends a    first distance radially from the turbine case and a second fin    extends a second distance radially from the turbine case, and    wherein the first distance is unequal to the second distance.

14. A system comprising:

-   a turbine case for a gas turbine engine;-   a plurality of turbine blades configured to rotate within the    turbine case; and-   a plurality of fins arranged on the turbine case, the fins extending    radially from the turbine case, each of the fins comprising a means    for maintaining a tip clearance, the tip clearance being a distance    between a blade track and tips of the turbine blades as the tips    pass the blade track.

15. The system of aspect 14, wherein the fins are attached to a flangeat an edge of the turbine case.

16. The system of aspect 14, wherein the fins are non-polyhedron.

17. The system of aspect 16, wherein the fins are cylindrical, wherein afirst fin of the plurality of fins has a first radius and a second finof the plurality of fins has a second radius, and wherein the firstradius is greater than the second radius.

18. The system of aspect 14, wherein a first fin of the plurality offins has a first shape and a second fin of the plurality of fins has asecond shape, and wherein the first shape is different from the secondshape.

19. The system of aspect 18, wherein the first shape comprises acylinder and the second shape comprises a polyhedron.

20. The system of aspect 14, wherein the turbine case has a length in anaxial direction of the turbine case, and wherein the turbine casecomprises a first flange and a second flange, wherein at least one finof the plurality of fins extends from the first flange to the secondflange.

What is claimed is:
 1. An apparatus comprising: a protrusion on aturbine case, the protrusion comprising a means for maintaining a tipclearance, the tip clearance being a space between a blade track and atip of a turbine blade configured to rotate within the turbine case. 2.The apparatus of claim 1, wherein the protrusion is included in aplurality of protrusions on the turbine case that each comprise acorresponding means for maintaining the tip clearance.
 3. The apparatusof claim 2, wherein the protrusions comprise a first protrusion and asecond protrusion, the first protrusion extends a first distanceradially from the turbine case and the second protrusion extends asecond distance radially from the turbine case, wherein the firstdistance is greater than the second distance, wherein the turbine caseincludes a first portion comprising a first local mean thermal inertiaand a second portion comprising a second local mean thermal inertia,wherein the first local mean thermal inertia is greater than the secondlocal mean thermal inertia, and wherein the first protrusion is locatedon the first portion and the second protrusion is located on the secondportion.
 4. The apparatus of claim 2, wherein the turbine case includesa first portion comprising a first local mean thermal inertia and asecond portion comprising a second local mean thermal inertia, whereinthe first local mean thermal inertia is greater than the second localmean thermal inertia, and wherein the first portion comprises a greaternumber of protrusions than the second portion.
 5. The apparatus of claim1, wherein the protrusion has a height and a length, and wherein themeans for maintaining tip clearance is configured to transfer heat fromthe turbine case to an ambient fluid, the heat transfer occurring at arate, the rate varying with the height of the protrusion, the heightvarying along the length.
 6. The apparatus of claim 1, wherein theprotrusion is integral to the turbine case.
 7. The apparatus of claim 1,wherein the protrusion is a first protrusion, and wherein a secondprotrusion comprising a means for maintaining a tip clearance issituated on a structure supporting the blade track, wherein thestructure supporting the blade track is located radially inward from theturbine case.
 8. An apparatus comprising: a turbine case comprising afin, wherein the fin comprises a protrusion extending a height radiallyfrom the turbine case and a width circumferentially along a surface ofthe turbine case, the fin extending a length along an axial direction ofthe turbine case, the length larger than the width.
 9. The apparatus ofclaim 8, wherein the fin is included in a plurality of fins, and thefins are distributed non-uniformly around the case.
 10. The apparatus ofclaim 8, wherein the fin extends radially inwardly from the turbinecase.
 11. The apparatus of claim 8, wherein the fin extends radiallyoutwardly from the turbine case.
 12. The apparatus of claim 8, whereinthe height varies along the length.
 13. The apparatus of claim 8,wherein the fin is included in a plurality of fins on the turbine case,wherein a first fin extends a first distance radially from the turbinecase and a second fin extends a second distance radially from theturbine case, and wherein the first distance is unequal to the seconddistance.
 14. A system comprising: a turbine case for a gas turbineengine; a plurality of turbine blades configured to rotate within theturbine case; and a plurality of fins arranged on the turbine case, thefins extending radially from the turbine case, each of the finscomprising a means for maintaining a tip clearance, the tip clearancebeing a distance between a blade track and tips of the turbine blades asthe tips pass the blade track.
 15. The system of claim 14, wherein thefins are attached to a flange at an edge of the turbine case.
 16. Thesystem of claim 14, wherein the fins are non-polyhedron.
 17. The systemof claim 16, wherein the fins are cylindrical, wherein a first fin ofthe plurality of fins has a first radius and a second fin of theplurality of fins has a second radius, and wherein the first radius isgreater than the second radius.
 18. The system of claim 14, wherein afirst fin of the plurality of fins has a first shape and a second fin ofthe plurality of fins has a second shape, and wherein the first shape isdifferent from the second shape.
 19. The system of claim 18, wherein thefirst shape comprises a cylinder and the second shape comprises apolyhedron.
 20. The system of claim 14, wherein the turbine case has alength in an axial direction of the turbine case, and wherein theturbine case comprises a first flange and a second flange, wherein atleast one fin of the plurality of fins extends from the first flange tothe second flange.